linux-kernel - Re: [PATCH 0/5 v2] Fixes for leapsecond expiring early ABS_TIME CLOCK

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Date:	Fri, 12 Jun 2015 11:06:07 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Dave Jones <davej@...emonkey.org.uk>,
	John Stultz <john.stultz@...aro.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Prarit Bhargava <prarit@...hat.com>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Jan Kara <jack@...e.cz>, Jiri Bohac <jbohac@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [PATCH 0/5 v2] Fixes for leapsecond expiring early ABS_TIME
 CLOCK_REALTIME timers

On Fri, Jun 12, 2015 at 10:58 AM, John Stultz <john.stultz@...aro.org> wrote:
> On Fri, Jun 12, 2015 at 7:52 AM, Dave Jones <davej@...emonkey.org.uk> wrote:
>> On Thu, Jun 11, 2015 at 03:54:52PM -0700, John Stultz wrote:
>>  > So this is a second round at trying to address the issue, trying
>>  > to integrate feedback from Ingo and Thomas, trying to simplify
>>  > what I can. I've also split out the changes so each can be
>>  > more easily reviewed. Its still not tiny, but its simpler.
>>  >
>>  > This series is against tip/timers/core, and the first patch isn't
>>  > strictly related but is a fix that is needed in tip/timers/core.
>>  >
>>  > As Prarit reported here:
>>  > https://lkml.org/lkml/2015/5/27/458
>>  >
>>  > Since the leapsecond is applied at timer tick time, and not
>>  > the actual second edge, ABS_TIME CLOCK_REALTIME timers set for
>>  > right after the leapsecond could fire a second early, since
>>  > some timers may be expired before we trigger the timekeeping
>>  > timer, which then applies the leapsecond.
>>  >
>>  > Thus this patch series tries to address this issue, including
>>  > extending the leap-a-day test to catch this problem, as well
>>  > as other relevant fixups I found while working on the code.
>>  >
>>  > This series has only had limited testing, so I wanted to send
>>  > it out for initial review and comment. Folks can grab this tree
>>  > via git for testing here:
>>  > https://git.linaro.org/people/john.stultz/linux.git dev/early-leap-timer
>>
>> Any idea how far back this reaches ? Ie, which longterm stable releases
>> might be affected by this ?
>
> I suspect all the way back to where hrtimers were introduced and
> possibly further.
>
>> (It really creeps me out that we're still changing this code so close
>>  to the next leap second event).
>
> Yea. This isn't something I'm suggesting folks deploy for the end of
> this month. It likely will be 4.3 material.

Well, noticing the -tip merge messages in my inbox, it may actually
make it for 4.2 (after all the push-back from last time, I expected
there would still be more), but still not something I'm wanting to
aggressively push to -stable.

thanks
-john
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